The present invention relates to gas analyzers, such as an infrared ray gas analyzer of the non-dispersion type or an ultraviolet ray gas analyzer of the non-dispersion type which are used for measuring the concentration of carbon monoxide or the like in air.
Conventional infrared gas analyzers of the non-dispersion type are shown in FIG. 1 and FIG. 2. FIG. 1 shows a gas analyzer of the non-dispersion type which employs a double light path and intermittent light and which includes light source or sources 44, revolving sector 45, reference cell 46, measurement cell 47 and detector 41. Although various types of detectors have been used, a pheumatic detector employing a condenser microphone will be described herein. In order to eliminate the influence of changes in the surrounding temperature upon detector 41, separate right and left chambers 42 are provided with connecting leak opening 43 therebetween, so that there will always be a static pressure equilibrium therebetween. Thus, detector 41 can sense only dynamical pressures having short cycles. In order to realize this, revolving sector 45 is provided which intermittently emits infrared rays from light source 44 at constant intervals. Furthermore, gases such as nitrogen which do not absorb infrared rays are enclosed in a reference cell 46. Zero gas is put into a sampling cell 47, and then the energy of infrared rays reaching the respective chambers 42 of detector 41 is kept balanced, and moreover their phases are so equalized that the output of detector 41 may be adjusted to zero. Then, a test gas is introduced into sampling cell 47. If the test gas absorbs the energy of the infrared rays passing through sampling cell 47, a difference will occur between the energy of infrared rays which pass through sampling cell 47 and the energy of infrared rays which pass through reference cell 46. This difference of energy levels leads to the generation of an unbalanced pressure signal synchronized with the cycles of revolving sector 45 between the respective chambers 42 of detector 41. The concentration of a specified gaseous component in the test gas can be measured by the indication of an indicator 47 against an amplified such pressure signal.
However, in this method a slight break in energy balance between the respective chambers 42 of the optical system operates to negate the high degree of stability necessary in a high sensitive region. This is the reason why this method is not suitable for measuring gaseous components of particularly small amounts. Because a remarkably high precision in the balance of energy is required, zero adjustment of detector 41 to achieve equalization of phases is necessary, and such adjustment is troublesome and time-consuming. Furthermore, expensive apparatus is required for carrying out such adjustment. In addition, there also exists the problem of maintenance, since the device includes mechanically movable parts.
FIG. 2 shows a single light path gas analyzer of the non-dispersion type in which the intermittent light method is employed without using the reference cell and the revolving sector described in the above mentioned example. In this arrangement, 51 is a sampling cell and 58 is a detector. Although various types of detectors have been used, a pneumatic detector will be described herein. The test gas and the standard gas (for example, zero gas) are alternately introduced into sampling cell 51 by operating pressure regulators 53a and 53b and needle valves 54a and 54b, respectively, and by alternately opening and closing three-way electromagnetic valves 52a and 52b. At first infrared rays emitted from a light source 55 are not absorbed while sampling cell 51 is filled with zero gas. On the other hand, the special gaseous component in a test gas absorbs infrared rays while the test gas is introduced int sampling cell 51. Thus, a condenser membrane 57 provided in the separated chamber 56 is pressurized, and the static capacity of the condenser is altered at a constant cycle synchronized with a changeover cycle of three-way electromagnetic valves 52a and 52b. The concentration of the gaseous component is measured by electrically measuring such change in the static capacity of the condenser.
But, although this single-cell type of arrangement can overcome the defects of the above mentioned gas analyzer of FIG. 1 to some degree, the length of the sampling cell is increased in order to measure the special gaseous components which are contained in the test gas in a specially small amount because the quantity of infrared rays absorbed is in proportion to the length of the cell, and thus also the space for receiving gas in sampling cell 51 is increased. Therefore, the quantity of the test gas or zero gas introduced into sampling cell 51 is increased enormously in the measurement of gaseous components of a small amount. For example, in the measurement of carbon monoxide in air, the length L of cell 51 must be 30 to 50 cm, and the space V for receiving gas must be 90 to 150 cm.sup.3. If a frequency of 5 Hz is used in detector 58, the test gas or zero gas must be introduced into sampling cell 51 at a ratio of 27 to 45 liters/min. Thus, a pump of a great capacity is required and therefore a large scale apparatus is required. This leads to the problem of high costs. A gas analyzer of this type has a defect in that it has no practical use because a supply of zero gas of great volume is required in addition to the above mentioned troublesome problems.